Rotation monitor protection system for p.p.i. display tube



Feb- 1, 1966 N. T. SIMOPOULOS ROTATION MONITOR PROTECTION SYSTEM FORP.P.I. DISPLAY TUBE Filed May 29, 1965 INTENSITY CUT-OFF CONTROL-28V.D.C

FIG-1 FIG-2 INVENTOR NICHOLAS T. SIMOPOULOS wwww ATTORNEYS United;States Patent 3,233,141 ROTATION MONITOR PROTECTION SYSTEM FOR P.P.I.DISPLAY TUBE Nicholas T. Simopoulos, Dayton, Ohio, assignor to DaytonElectronic Products Company, Inc., Dayton, Ohio, a corporation of OhioFiled May 29, 1963, Ser. No. 284,174

7 Claims. (Cl. 315-) This invention relates to a cathode ray tubeprotection device and more particularly to an apparatus and a circuitfor protecting the tube phosphor from damage due to the cessation ofmovement of a trace or beam which movement is dependent upon thecontinued movement of a '"rnemb'er' external to the 'tube.'

*This invention is particularly adapted and useful for the protection ofthe phosphor of cathode ray tubes which are employed to reproduce orsimulate a position of a {moving or a rotary member. Such a cathode ray'tube ir 'stallation may have a P.P.I. presentation witha rotat- "in'gsweepwhich is generated by a-rotating yoke tructure. fIfi-for' anyreason, the yoke should fail to rotate, the phosphor of the tube'wouldbe damaged or burned in a short ams-by the electron beam, in the absenceof a protective arrangement. It is therefore a primary object of this"invention to provide a cathode ray tube protecting device for tubeswhich have beams or traces which depend. for their movement on themovement of another member and whic'hfdevice is responsive to thecessation of movement of-such inember external to the tube to remove orotherwise blockth e trace'from the cathode ray tube. '"f "A notiiler-lobject 'of this invention is'to provide a cathtbde 'raiitubfe protectingdevice which is positive in opratioir'to prevent damage to the tubephosphor upon the surrea jor conditions which" would otherwise permit*thejelctroris todamage the phosphor.

further object'of this' invention is the-provision of a'eathoder aytube-protecting device for a CRT tube employing a'rotating yoke. 3 Astill further object of this invention is the provision f ofa'cathod'eray tube protecting device wherein a photoconductive transducer, such asa photosensitive diode, is arran ed with respect to a light modulatingor chopping device and a light source to sense cessations-of movement ora rotating yoke to remove or block the trace from the screen-of thetube, and to reapply the trace upon the recurrence of yoke rotation;

These and other objects and advantages of the invention 'willbejapparent from the following description, the acc'om'pa'nying'drawings and the appended claims.

In the drawingsi FIG. 1 isa diagram of a preferred embodiment of theinvention; and

FIG. 2 is awiring diagram of' the electrical portion of the device ofFIG. 1. I

, Referring to the figures of the drawing, a cathode ray tube which isprotected by this device is somewhat diagrammatically illustrated at 10in FIG. 1 as including the usual face or screen 12 and neck 13. Adeflection yoke 14 is surmounted over the neck 13 and includes means(not shown) .mounting the yoke 14 for rotation. The cathode ray tube 10may, for instance, form part of apparatus for simulating or followingthe movement of a radar antenna, and displaying P.P.I. traces, such asthe trace shown at 15, which effectively rotate angularly v to rotatethe yoke 14 through suitable reduction gearing 3,233,141 Patented Feb.1, 1966 ice about the center axis of the tube in synchronism with therotation of a radar search antenna. A specific example is the tubeincorporated within a video mapping set which forms a luminous rotatingtrace for the purpose of projection through a transparency or a mapwhich is then displayed by superimposition on an operators radar scope.The simulation and reproduction of the search antenna position isprovided on the cathode ray tube in part by a deflection yoke which isrotated. through a suitable reduction drive in synchronism with theantenna drive.

In such CRT installations where spot or trace movement is dependent uponthe continued movement of another member, such as a search antenna, theantenna may stop or cease to rotate. Even though this stoppage may betemporary, if it persists more than a minute or so, it may be sufiicientto cause the tube 10 to be damaged. This invention provides means whichis responsive to the continued rotation of the yoke 14 and whichoperates upon the cessation of yoke rotation to remove the trace, suchas by removing the Z axis input at the grid of the 'tube, 'by biasingthe tube gun below cutoff, removing anode voltage, or any other meansconvenient to protect the phosphor.

Thus, a motor 20, which may .be synchronously controlled by any meanswell known in the art, is connected reflecting surfaces 32 are formed.The light source 25 and transducer 26 are positioned with respect to thewheel 31 so that the rotation of the wheel 31 causes the light from thesource 25 to sweep across the transducer 26 thereby chopping ormodulating the light falling on the transducer. It isobvious that otherarrangements may be used for the interrupter 30, such as a slotted orsegmented disk, or'a scanner With multi-sided planar reflector surfaces.

The output of the transducer 26 is applied to an intensity cutolfcircuit indicated generally at 35 which, upon cessation of rotation ofthe wheel 31, operates to block or remove the trace 15 from the screen,such as by blocking the'Z axis input.

Referring to FIG. 2, the power supply for the lamp 25 is shown asincluding a -28 volt D.C. supply, a dropping resistor 38 and a smallfilter capacitor 39. The transducer 26 may be of any suitable type whichundergoes a change of resistance with a change in intensity oflightfalling thereon, and a photoconductive diode of the type 1N2175 may beused. A volt DC. power supply for the diode 26 is applied throughvoltage dividing resistor 40 and potentiometer 41, load resistor 42 anda lead 43. The voltage adjusting potentiometer 41 determines theoperating bias on the diode 26.

The change in voltage developed across the load resistor 42, due to thechange in resistance of the diode 26, is reflected at the couplingcapacitor 50 essentially as a a) square wave which is amplified. in thetube section 52A and capacitively coupled through a capacitor 53 to thejunction of a pair of series-connected diodes 55 and 56. The diodes 55and 56 lead from the grid of the tube section 523 to ground and thusform a DC). rectifying circuit for the varying or changing diode 26output and. which holds the grid of the tube section 52B below cutolf aslong as the member 30 and yoke 14 are rotating. The tube section 528 maybe considered as a current control device which is held inoperativeduring the detection of modulated signals from the transducer.

Controllable switch or circuit means effective to block the traceincludes a control relay 60 which is connected in series with the plateof the tube portion 523 and which is normally unenergized due to thecatch condition of this tube section. The relay 60 including normallyclosed contacts 62 which form a closed circuit path for the z axis inputto the cathode ray tube. However, upon the cessation ofpulses to thetube 52 signalling the stoppage of the antenna, the relay 65 isenergized to open or block the Z axis input thus removing the trace 15from the face of the cathode ray tube.

The operation of the invention described is mainly selfcvident from theforegoing description. The motor 20 will normally operate in synchronismwith the radar antenna and rotate the yoke 14 through suitable gearing,such as the reduction gearing 22. The light falling on the photo-diode26 will be modulated by means of the individual reflectors 32intercepting the light from the lamp 25 with the rotation of the Wheel30. The changing output of the diode 26 is amplified in the tube section52A and detected by the diodes and 56 to hold the tube section 52B belowcutoff. If, for any reason, the motor 20 should cease to drive the yoke14, a steady state condition is caused at the diode 26, thus operatingthe relay 60 through the tube 523 and removing the Z axis input to thetube. in this manner, the phosphor on the screen of the tube isprotected against electron burn. However, just as soon as the motoragain operates, the relay 60 is automatically released by the grid ofthe tube section 52B being driven to cutoff, and the Z axis input isreapplied to the tube 10.

It will therefore be seen that this invention provides a cathode raytube protecting device Which is both positive and automatic in itsoperation. It may be incorporated into compact equipment with a minimumof space requirements.

While the form of apparatus herein described constitutes a preferredembodiment of the invention, it is to be understood that the inventionis not limited to this precise form of apparatus, and that changes maybe made therein without departing from the scope of the invention whichis defined in the appended claims.

What is claimed is:

1. A cathode ray tube protecting device wherein movement of the electronbeam on the phosphor screen is controlled by a rotary member, theimprovement comprising light-interrupting means connected to rotate Withsaid member, a light source directing a beam of light for interruptionby said interrupting means, a photoelectric transducer positioned toreceive interrupted light when said member is turning and to receive asteady state light condition when said member is stationary, and controlcircuit means connected to said transducer and responsive to the absenceof a changing output signalling the cessation of movement of said memberto remove said beam from said cathode ray tube.

2. A cathode ray tube protecting device wherein movement of the electronbeam on the phosphor screen is controlled by a rotary member, theimprovement comprising light-interrupting means connected to rotate withsaid member, a light source directing a beam of light for interruptionby said interrupting means, a photoelectric transducer positioned toreceiver interrupted light when said member is turning and to receive asteady state light con 4 dition when said member is stationary, controlcircuit means connected to said transducer and responsive to the absenceof a changing output signalling the cessation of movement of said memberto remove said beam from said cathode ray tube, and further responsiveto a re-establishment of said changing output signalling the resumptionof rotation of said member to reestablish said beam.

3. A cathode ray tube phosphor protecting device for preventing aphosphor burn in a cathode ray tube where a trace on the tube is movedin synchronism with an externally rotated member, comprising a lightsource, a photoconductive transducer, a light modulating wheel rotatedin response to the rotation of said member and effectively interposedbetween said light source and transducer to modulate the light fallingthereon from said source upon the rotation of said member and providingan essentially steady state condition upon the cessation of memberrotation, means connected to receive the output of said transducer, andcontrol means responsive to the absence of a change in said output forremoving said trace from said cathode ray tube.

4. A cathode ray tube phosphor protecting device for preventing aphosphor burn in a cathode ray tube where a PPI trace on the tube isswept radially and rotated by a rotating yoke on said tube, comprisingmeans normally rotating said yoke, a light source, a photoconductivetransducer, a light modulating device connected for rotation by saidyoke rotating means and efiectively interposed between said light sourceand transducer to modulate the light falling thereon from said sourceupon the rotation of said yoke and providing an essentially steady statecondition upon the cessation of yoke rotation, means connected toreceive the output of said transducer, and control means responsive tothe absence of a change in said output having controllable switch meansconnected to remove said trace from said cathode ray tube upon saidcessation of yoke rotation.

5. A phosphor protecting device for a cathode ray tube having a rotatingyoke and arranged to simulate the position of a radar search antenna forpreventing phosphor burn in the event that the search antenna isstopped, comprising drive means for rotating said yoke in synchronismwith the rotation of said antenna, means defining a light source, aphotoconductive transducer, a light modulating wheel connected forrotation with said yoke drive means and elfectively interposed betweensaid light source and transducer to modulate the light falling thereonfrom said source upon the rotation of said drive means and providing anessentially steady state condition upon said transducer with thecessation of drive means rotation signalling the cessation of antennamovement, detector means connected to receive the output of saidtransducer, and relay control means responsive to the failure of achange in transducer output connected to remove the trace from saidcathode ray tube upon said failure and further responsive to theresumption of changing transducer output signalling resumption ofantenna movement to reestablish said trace.

6. A cathode ray tube phosphor protecting device for protecting thephosphor of a cathode ray tube including a rotating deflection yoke,comprising a rotating reflector member connected in driven relation tosaid yoke, a light source, a photoconductive transducer positioned tointercept from said source a light swept by said member upon therotation thereof, an amplifier connected to said transducer to amplifythe signal therefrom, a detector connected to said amplifier, a currentcontrol device connected to said detector and normally held inoperativeduring the detection of modulated signals from said transducer, andcontrollable switch means connected for operation by said currentcontrol device and operable upon the cessation of detection of saidmodulated signal to remove the trace from said cathode ray tube.

"1'. A cathode ray tube phosphor protecting device for protecting thephosphor of a cathode ray tube including a rotating deflection yoke,comprising a rotating light modulating member connected to rotate Withsaid yoke, 21 light source, a photoconductive diode positioned toreceive from said source a light modulated by said member upon therotation thereof, an amplifier connected to said transducer to amplifythe signal therefrom, a rectifier connected to said amplifier, a controltube having a grid connected to said rectifier and normally held atcutoff during the detection of modulated signals from said transducerduring rotation of said yoke, and a relay connected for operation bysaid control tube and operable with the conduction of said control tubeupon the cessation of 6 detection of said modulated signal to open acircuit effective to remove the trace from said cathode ray tube, and toclose said circuit upon the reestablishment of yoke rotation.

References Cited by the Examiner UNITED STATES PATENTS 2,401,432 6/1946Luck 315-27 X 2,404,147 7/1946 Strickland 250215 X 2,882,445 4/1959Sprengeler et a1 315-20 DAVID G. REDINBAUGH, Primary Examiner.

1. A CATHODE RAY TUBE PROTECTING DEVICE WHEREIN MOVEMENT OF THE ELECTRONBEAM ON THE PHOSPHOR SCREEN IS CONTROLLED BY A ROTARY MEMBER, THEIMPROVEMENT COMPRISING LIGHT-INTERRUPTING MEANS CONNECTED TO ROTATE WITHSAID MEMBER, A LIGHT SOURCE DIRECTING A BEAM OF LIGHT FOR INTERRUPTIONBY SAID INTERRUPTING MEANS, A PHOTOELECTRIC TRANSDUCER POSITIONED TORECEIVE INTERRUPTED LIGHT WHEN